Power up like normal and have the system in neutral. Press and hold the set button until it starts to flash, it should go through 13 flash cycles before you get to the sensor test. The LED colors will be Blue, Yellow, and Red. (Yellow and Red flash before this one so you have that as a warning)
Once you are in test mode you just rotate the motor. The LED's on will Rotate through a Blue, Yellow, Red cycle. So Blue will light up, then Blue/Yellow, then Yellow, then Yellow/Red, then Red, the Red/Blue, then it repeats.
I just did this about 2 weeks ago when troubleshooting my esc. The sensor test worked, but the esc was still toast.